1. Field of Invention
This invention relates to the field of display devices, particularly active display devices, formed by small light emitting elements (pixels), the aggregate of which forms a display image, including characters, and in particular to the displays which are organized in pixels which are typically arranged in rows and columns over the surface of the display area, sometimes as a checkerboard (x-y arrangement or chess-board). The invention discloses a method and a system to forestall the formation of continuous lines of light elements, often distinguishable in the image, which are visually disturbing because the true image is continuous with no streaks across it.
2. Discussion of Prior Art
For better understanding of the description that follows we want to clearly define some terms used in what follows. Artifact: as used here and in technology, the term means an unwanted, and usually undesirable and deleterious change on the result produced as a consequence of the particular method used to measure or to detect something. In this sense the term is used mostly by researchers in laboratories and departs from the ordinary English dictionary meaning of it. Variously spelled as “artifact” and “artefact”.
Checkerboard arrangement: a horizontal-vertical arrangement of squares, as the ones on a checkerboard or chess board or tic-tac-toe grouping of squares. Used here to indicate an equivalent arrangement of pixels (q.v.), also called here x-y arrangement or a matrix type arrangement. If the notation x-y is used, usually x—lies along the horizontal direction (or rows) and y—lies along the vertical direction (or columns). Cf With 2-D hexagonal close-packed arrangement (2Dhcp), with pseudo hexagonal close-packed arrangement and with pseudo-checkerboard arrangement.
2-D Hexagonal close-packed arrangement (2Dhcp): On a surface described by a standard x-y Cartesian coordinate system, the 2Dhcp is a geometrical distribution of equal circular elements on a surface such that subsets of the equal elements are arranged on horizontal lines characterized by the same y-coordinate, and each horizontal line is occupying such a position that the x-coordinate of each of its elements is at the average horizontal (x) coordinate as the coordinates of the elements to its right and left on the lines just above and below it. The 2dhcp arrangement packs the maximum number of circles on any given surface. Cf Checkerboard arrangement and pseudo hexagonal close-packed arrangement and pseudo checkerboard arrangement.
Line of pixels: We arbitrarily define a line of pixels as a straight line passing by a plurality of light emitting device pixels within the centers of the pixels plus or minus 5% (5 percent) of the radius of the pixels.
Neighborhood of a pixel: We arbitrarily define here the neighborhood of a light emitting device pixel as a circle around the center of the light emitting device pixel with radius equal to 5% (5/100) of the distance between the two closest of the light emitting device pixels of the set.
Pixel (also light emitting device pixel): An elementary light emitter which is small enough that it is hardly distinguishable from its neighbor pixels from the intended viewing distance. A pixel may be a combination of several individual light emitters of different colors, as red-green-blue (RGB), in which case it is the group that is considered a pixel, instead of an individual light emitter. Also used for an elementary light detector, as a the individual light detectors in a digital camera. Associated with Pixelized: the quality of a image or display which is made from pixels.
Position of pixel: We call the position of each pixel as the point where is located the geometric center of the single or multiple light emitting devices corresponding to the pixel.
Pseudo checkerboard arrangement: An arrangement of light emitting device pixels which includes one or more deviations from the checkerboard arrangement. Variations may include two rows (or lines) following an hexagonal close-packed arrangement, two rows (or lines) at a distance larger than the minimum distance characteristic of the checkerboard arrangement, or other partial departure from the true checkerboard arrangement. Such internal departures from the ideal contribute to forestall line continuations from one module to the neighboring module(s). Cf hexagonal close-packed arrangement, pseudo hexagonal close-packed arrangement and with checkerboard arrangement.
Pseudo hexagonal close-packed arrangement: An arrangement of light emitting device pixels which includes one or more deviations from the hexagonal close-packed arrangement. Variations may include two rows (or lines) following a checkerboard arrangement, two rows (or lines at a distance larger than the minimum distance characteristic of the hexagonal close-packed arrangement, or other partial departure from the true hexagonal close-packed arrangement. Such internal departures from the ideal contribute to forestall line continuations from one module to the neighboring module(s). Cf Hexagonal close-packed arrangement, with checkerboard arrangement and pseudo checkerboard arrangement.
Radius of the pixels: We arbitrarily define the radius of a pixel as the smallest distance between a pixel and any of its neighbors.
The field of pixelized displays has been characterized by displays which consisted of light elements (pixels) usually arranged in repeating rows and columns, as a matrix (or x-y, or checkerboard). The rows and columns are usually evenly spaced, but sometimes the horizontal (x) separation is not the same as the vertical (y) separation. This choice of evenly spaced horizontally and vertically arranged pixels occurred because it is less expensive and easier to manufacture such a type of display on such an organized array than a display with randomly positioned pixels, as are, for example, the pixels on a pointillist painting by Georges Seurat, in which the individual dots were randomly arranged, besides being of variable size. The economic advantage of smaller price of manufacture comes at the price of decreased image quality—after all, there was a good reason, a very good reason indeed, why Seurat and the other pointillist painters never used colored dots on evenly spaced rows and columns as current manufactured lighted displays do. But alas, theirs was a work of art, while pixelized light emitting displays are work of money! Still, one is tempted to improve the quality of displays made for money—how much better life would be if billboards displayed works of art instead of advertisements for products that are not even needed. It is difficult to improve on Seurat's paintings, but it is easy to improve on the poorly conceived work of money—though the inventors can't help other than to wonder if it is worth to do this, to improve the visual quality of advertising boards.
FIG. 1 shows a simplified example of existing devices (old art in patent attorneys' parlance) pixelized display. FIG. 1 depicts very very few pixels for simplicity. In it one sees a simplified display of the type used for outdoor advertisement in the United States: a vertically oriented display designed for street announcements, typically measuring 20 meters horizontally by 5 meters vertically. The light emitting elements (pixels) may be spaced 1 cm center-to-center, spaced in both the horizontal and vertical dimensions, making a total of 2,000 by 500 pixels for a display measuring 20 meters wide by 5 meters high (approximately 60 ft by 15 ft), but these are just typical dimensions, actual values varying substantially from model to model, these values not being used to limit my invention, but only to give a general idea of the typical existing devices. In the simplified display shown at FIG. 1 there are 15 pixels on the horizontal direction and 12 pixels on the vertical direction, the display made on an arrangement of 18 modules, each module having 10 pixels with 2 rows and 5 columns each. Most of the existing street announcing devices use LEDs with brightness from 5,000 to 10,000 cd/m-squared, but this is not a limitation of the current invention. The display is supported in the vertical position by a suitable structure located behind and around it, behind and around the light emitting surface, which is then freely visible from the front of the display. The supporting structure behind the light emitting elements also carry the electrical power wires and all the required electronics. A controlling computer is usually at the ground, in a more accessible location than the display, which typically is high to increase visibility.
The light emitting surface is typically subdivided in modules that are designed for easy industrial production, typically of rectangular or square shape. These modules may typically have dimensions of the order of a foot (30 cm), for example, 20 cm by 40 cm. FIG. 1 displays rectangular modules as an example. Each module is in turn composed of a large number of relatively small light emitters, typically three types of emitters, capable of emitting three distinct colors, typically red, green and blue (RGB), but variations are possible and in use, 2 reds, 1 green and 1 blue per pixel or RRGB, also RGB with a white LED, or RGBW being very common. Inside each module, the light emitters, or pixels, are usually arranged in rows and columns, and the modules themselves are arranged in rows and columns too, as per FIG. 1, so the whole arrangement creates various levels of rows and columns of light distribution. As described below, out invention discloses a method and a system to break these lines of light. In FIG. 1 the modules are rectangular with 2 rows and 5 columns of pixels.
FIG. 2 depicts the visual effect of a line with a small inclination with the horizontal direction. Due to the small inclination (slope in mathematics), what is a slowly increasing y-coordinate is depicted with the same y-coordinate for several contiguous pixels, forming a short horizontal line, the full line being then depicted as a series of short horizontal steps which are visually disturbing to the viewer for being so unnatural.
Isaac Newton was the first to notice that an appropriate mixture of three colors is capable of creating the visual impression on humans of all the colors, which he demonstrated with his Newton color wheel, a fact that today is easy to predict once it is know that the human eye (and many other mammals as well) has three types of different cone shaped detectors capable of responding to three different colors—actually three different maximum responses at three different colors, which overlap. For lighted advertising displays, designed to prod people to buy objects that they do not need, an appropriate combination of each of these colors at a continuously varying light intensity, is capable of creating a suitable variety of colored dots, the aggregate of which produces an image when viewed from and beyond a certain distance, which depends on the size of the pixels used for the display.
As examples of the decreased image quality we can cite:
1. if a particular feature falls on a line that also happens to be thin and horizontal, the display procedure could consider the lighted points to fall in between the existing pixels and ignore the line, which would then not be shown, or could display it using all pixels above the actual line and all pixels below the actual line, therefore increasing the line width, or could display it at a horizontal line just under the correct position, all options creating a deformed image.
2. same, mutatis mutandis, for a vertical line,
3. if a particular feature falls on a line which is at a small angle with the horizontal, given the impossibility of displaying points (pixels) at arbitrary vertical positions, the display would have to light a small horizontal segment followed by another small horizontal segment slightly higher, etc., etc., which causes a disturbing image of a stairway,
4. same, mutatis mutandis, for an off-vertical line.
The last two effects are disturbing because our brains are trained to detect the stair-case feature out of the background. It would be advantageous to have a display system that were not characterized by these artifacts.